The process of the present invention relates to monovinylidene aromatic polymers.
Many desirable properties of monovinylidene aromatic polymers are dependent upon the weight average molecular weight (Mw) of the polymer, wherein higher molecular weights provide better properties. The problem which arises with high molecular weight polymers is that of processability. Typically, high molecular weight polymers have high viscosities, making them difficult to process. Processing at higher temperatures will lower the viscosity, but in most circumstances the high temperatures needed for desirable viscosities cause polymer degradation as well.
U.S. Pat. No. 3,678,016 discloses a process wherein crosslinking addition reactions are reversible at elevated temperatures so that polymer-curing agent compositions can be maintained as fluid compositions at such elevated temperatures, long enough to be fabricated into shaped articles, and the fabricated articles are then set by cooling. However, this process requires two separate components maintained at very high temperatures (200-300xc2x0 C.) and long reaction times, which still lead to polymer degradation.
Therefore, there remains a need for a polymer composition having a high molecular weight, enhanced processability and good balance of mechanical and thermal properties.
The present invention relates to a high molecular weight monovinylidene aromatic polymer produced by polymerizing a vinyl aromatic monomer in the presence of a small amount of furfuryl (alkyl)acrylate.
Surprisingly, the incorporation of a small amount of furfuryl (alkyl)acrylate allows the monovinylidene aromatic polymer to be rheologically modified such that it has high flow at elevated temperatures, yet maintains a high molecular weight and excellent mechanical and thermal properties, without polymer degradation.
Suitable vinyl aromatic monomers used to produce the monovinylidene aromatic polymer include, but are not limited to, those described in U.S. Pat. Nos. 4,666,987, 4,572,819 and 4,585,825, which are herein incorporated by reference. Preferably, the monomer is of the formula: 
wherein R is hydrogen or methyl, Ar is an aromatic ring structure having from 1 to 3 aromatic rings with or without alkyl, halo, or haloalkyl substitution, wherein any alkyl group contains 1 to 6 carbon atoms and haloalkyl refers to a halo substituted alkyl group. Preferably, Ar is phenyl or alkylphenyl, wherein alkylphenyl refers to an alkyl substituted phenyl group, with phenyl being most preferred. Typical vinyl aromatic monomers which can be used include: styrene, alpha-methylstyrene, all isomers of vinyl toluene, especially paravinyltoluene, all isomers of ethyl styrene, propyl styrene, vinyl biphenyl, vinyl naphthalene, vinyl anthracene and the like, and mixtures thereof. The vinyl aromatic monomers may also be combined with other copolymerizable monomers. Examples of such monomers include, but are not limited to acrylic monomers such as acrylonitrile, methacrylonitrile, methacrylic acid, methyl methacrylate, acrylic acid, and methyl acrylate; maleimide, phenylmaleimide, and maleic anhydride. In addition, the polymerization of the vinyl aromatic monomer may be conducted in the presence of predissolved elastomer, such as butadiene or isoprene homopolymer or copolymer, to prepare impact modified, or grafted rubber containing products, examples of which are described in U.S. Pat. Nos. 3,123,655, 3,346,520, 3,639,522, and 4,409,369, which are incorporated by reference herein.
Polymerization processes and process conditions for the polymerization of vinyl aromatic monomers are well known in the art. Although any polymerization process can be used, typical processes are continuous bulk or solution polymerizations as described in U.S. Pat. No. 2,727,884 and U.S. Pat. No. 3,639,372, which are incorporated herein by reference.
The polymerization can be conducted at any temperature at which a high molecular weight polymer will be produced. Suitable polymerization temperatures are from about 80xc2x0 C. to about 170xc2x0 C., preferably from about 110xc2x0 C. to about 160xc2x0 C., with about 115xc2x0 C. to about 150xc2x0 C. being the most preferred.
An initiator may optionally be used, such as azo compounds and peroxides. Exemplary peroxides include tert-butylperoxybenzoate, tert-butylperoxyacetate, di-tert-butylperoxide, dibenzoylperoxide, dilauroylperoxide, 1,1-bis-tert-butylperoxycyclohexane, 1,1,-bis-tert-butylperoxy-3,3,5-trimethylcyclohexane and dicumylperoxide.
Additionally, molecular weight regulators can also be used in the production of the polymers of the present invention, including ethylbenzene, n-dodecyl mercaptan, polystyrene dimers and trimers, acrylate and (alkyl)acrylate dimers and trimers and the like. Other additives which may be present include plasticizers such as mineral oil, polybutene and the like, and antioxidants such as hindered phenols.
The furfuryl (alkyl)acrylates useful in producing the high molecular weight monovinylidene aromatic polymers include furfuryl acrylates, furfuryl methacrylates, furfuryl ethacrylates and the like. Alkyl substituted furfuryl (alkyl)acrylates can also be used, wherein the furfuryl group is additionally substituted with a C1-C10 alkyl group such as methyl, ethyl, butyl, isobutyl, propyl, isopropyl, pentyl and the like, e.g. 2-(5-methylfurfuryl)methacrylate. Preferably, furfuryl methacrylate is used.
The amount of furfuryl (alkyl)acrylate used in the polymerization is an amount such that the resulting monovinylidene aromatic polymer is rheologically modified to give high flow at elevated temperatures, such as 180 to 280xc2x0 C., yet maintain a high Mw and good mechanical and thermal properties. Preferably from 0.1, more preferably from 0.3, most preferably from 0.5 to less than 3, preferably less than 2.9, more preferably less than 2.8 and most preferably less than 2.7 weight percent furfuryl (alkyl)acrylate is present, based on the total weight of the vinyl aromatic monomer and furfuryl (alkyl)acrylate. It has been surprisingly discovered that such monovinylidene aromatic polymers have enhanced flow and rheological properties, yet maintain high molecular weights and excellent physical properties.
Copolymers of furfuryl methacrylate and styrene have been disclosed in various references including European Polymer Journal, vol. 30, No. 4, pp. 489-494. However, the amounts of furfuryl methacrylate used, causes increased amounts of crosslinking and decreased processability. Unexpectedly, the applicants have found that small amounts as claimed herein, offer increased molecular weight with good flow and processability and excellent physical properties.
The molecular weight of the resulting polymer is dependent upon a number of factors including the temperature, the (optional) initiator concentration, and the time of reaction. The term molecular weight (Mw) refers to the weight average molecular weight as determined by gel permeation chromatography calibrated with narrow polystyrene standards and using a refractive index detector.
The molecular weight of the high molecular weight polymer formed is typically from 100,000 to 500,000, most preferably from about 120,000 to about 450,000, as measured by gel permeation chromatography. Polymers having molecular weights greater than 450,000 are undesirable because they are difficult to process. Polymers having molecular weights less than 100,000 will not have the desirable properties obtained by the present invention.
The high Mw monovinylidene aromatic polymer produced by the process of the present invention can be employed in applications where high molecular weight vinyl aromatic polymers are suitably used, such as foam sheet, films and injection molding processes. They can also be combined with polymers of differing Mw to make polymer compositions having a multimodal molecular weight distribution, preferably a bimodal molecular weight distribution, hereinafter referred to as bimodal compositions.
In one embodiment, the high molecular weight monovinylidene aromatic polymer is produced by polymerizing a composition consisting essentially of a vinyl aromatic monomer ath a small amount of furfuryl (alkyl)acrylate. The phrase xe2x80x98consisting essentially ofxe2x80x99 refers to the components which are essential in order to obtain the advantages of the present invention and any other components present would not significantly change the properties related to the inventive advantage.